[CM] something like let-set! for undefined vars?

Iain Duncan iainduncanlists at gmail.com
Sat Feb 6 17:06:01 PST 2021

Hi folks, I've been digging into S7s environment support and loving it. I
have implemented a really convenient pseudo-inheritance-through-delegation
setup for my process objects, and one thing I'm using is the let-set!
function to allow updating internal variables from outside if desired. My
little method looks like this (in side of a let inside a function)

(define (set sym val)
      ;; TODO this doesn't allow setting values that are not yet set
      ;; need to check if symbol is in let and then set it
      (let-set! proc-env sym val))

However, this of course errors if I try to use if and sym is not defined. I
tried mucking about with the defined?  predicate, but got confused by the
docs. If anyone can tell me how I can easily add to the above the
following, that would be lovely:

- if sym not defined in proc-env, define sym to val

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